Well, a lot of the basics on query letters and why the heck you'd WANT an agent are already covered, but considering I've just been through this and all the DOs and DO NOTs are fresh in my mind, I thought I'd share helpful thoughts on how to prepare for querying, what to keep in mind while querying, and what to do in the later stages of the game.

(This is excerpted from an article on my website.)

On Preparing to Query:

It should go without saying that your book should be complete, polished, and if possible, vetted by your critique partner(s) and/or editor(s). Before you contact someone wanting to know if they want to help sell your work, your work has to be ready to sell. (Yes, edits are inevitable once the professional part of your journey begins, but that's no excuse for querying with a first draft.)

Draft a synopsis first. You need one to two paragraphs describing your book; you might consider writing several, then sharing them with people you know and asking them which one they like best. When asked to give feedback on a synopsis, most average readers will be vague and say they "like it," but when given three to choose from, they tend to be better able to articulate what works for them and why. Which is what you need to know.

Research agents. The Association of Authors' Representatives (AAR) and Agent Query can help you find one that represents your genre; and Preditors & Editors, Writer Beware, and Absolute Write Water Cooler can help you make sure you're not falling for a scam. Some agents have blogs which can help you figure out what they are looking for--and what to avoid while querying them.

Pick out several agents you think would be a good match for you, draft your letter, and prepare to keep track of your successes and failures. I recommend either keeping a local document detailing your dates of submission/dates and status of reply OR using a utility like Query Tracker. (They have a good listing of agents too.)

You may consider preemptively constructing a one-page synopsis and a short author bio for yourself. These materials are often requested by agents--sometimes they even want it sent along with the query letter.

You may consider fashioning an e-mail address specifically for writing-related business--one that you don't share anywhere else. That way a) you always know it's a response if you get an e-mail there; and b) the agent doesn't have to read e-mail from SeXYb0mB178@yahoo.com. I also recommend against creating e-mail handles like WryterGrrl or anything goofy referencing your status as a writer. (I could see "AlisonWrites" or "NovelsByJim" being okay, but I recommend just creating one primarily made up of your name.)

Every query should be personalized to the agent--and I don't just mean finding the appropriate name to fill in at the top. Unless you're submitting your query through an automated form (or are told otherwise), make it clear that you have some familiarity with the agent's preferred areas of representation and throw in a sentence about why you think your manuscript is appropriate for their list.

Most agents appreciate it if you identify your genre and word count (word count should be to the nearest 1,000 words).

When you describe your project, try to make the one or two paragraphs devoted to the synopsis read a bit like the blurb on the back of a paperback. The most common mistake I've seen in people's query letters is that they include too much detail. Drop worldbuilding details naturally; don't take two sentences to explain how your world works. Introduce your character(s) quickly and try to set up a problem in the first half and a hint at how it might be solved in the second. But don't be too vague, either. A novel about a character "trying to find herself" is a lot less compelling than a novel about a character "struggling with dual identities."

Too many synopses read like "this happened, then this happened, then this happened." Give broad strokes, not step-by-step story elements. A synopsis isn't an outline, and in a query letter it isn't even a complete story synopsis.

Refrain from writing in a grandiose or purple style while explaining your book. If a person's heartbeat picks up reading about your character's dilemma or your amazing concept, it isn't going to be because you did such a good job pillaging your thesaurus.

Don't try to be cute. This is a business proposal, and while it's fine to be a little informal in some situations, leave the snark on the floor and don't joke about how your writing is awful or how the agent is probably glad to receive your query after so many bad ones. Don't use smileys or silly fonts or jazzy stationery. You want to stand out, but your concept and professionalism will do it.

If you decide to include a sentence or two about why you think audiences will connect with your book or why it will sell, don't talk like a reviewer. Be honest and say why your book's subject is hot or already has a niche audience (which should be identified). Don't try to tell the agent that your book is super awesome using phrases like "tour de force" or "brilliant new voice." You don't need to praise yourself. You'll look silly and make them think "Yeah, right."

If your book is similar to existing authors' work and you think it would be helpful to say so, don't compare yourself or your writing to those authors. Say that readers who liked those books may appreciate yours. Comparing yourself to a successful author is a bad idea. Let reviewers do that once you're published.

Keep the query short. You're coming into an agent's inbox trying to prove how quickly you can get someone's attention. If your query takes up more than one sheet of paper when you print it out, make your synopsis shorter. You can do it in one or two paragraphs and maybe a follow-up line.

If you don't have any publishing credits to mention in the query, don't try to make something that isn't a publishing credit sound like one. Something small like your school paper or a publication with token pay is fine; something like your internal book club newsletter or your local free 'zine is going to make you look like you're grasping at straws. Having publication credits does help you look like you might be worth taking a shot on, but it isn't necessary. This project's being your first novel or your first on which you sought representation is not going to be viewed as the kiss of death whatsoever.

On Submitting Material:

If you get an agent's attention and they ask to sample your work, get ready for a rejection if you don't have something really special at the beginning. Remember: if your work doesn't get interesting immediately, that doesn't mean it's obviously BAD, but an agent is a businessperson and only wants to take your work if it will SELL. This doesn't mean you should be cheap with attention-getting tricks; it just means the agent (and the reader, ultimately!) is not going to ask for more if you take too long to get started.

Format it how the agent wants. One thing you should be familiar with is Standard Manuscript Format. Don't use silly fonts. If the agent requests a standardized filename, use it.

Don't submit stuff they don't ask you to submit! Sometimes people will advocate being pushy or sending unsolicited material, but what that communicates is that you think you're above getting in line. If you're looking for an agent, you're theoretically hoping to aim for commercial success. That does require a certain amount of toeing the line. Your material itself might push the envelope, be subversive, be rebellious, etc., but YOU shouldn't be.

Before sending your letter or e-mail, check and double check the name of the agent and the spelling of the agency. Do it so you feel ridiculous with how thorough you're being . . . so you won't worry later that you did it wrong. If you are unsure of the gender of your intended agent, just write out the person's first and last name while querying.

What to Expect:

Agents work for free until they sell your manuscript. That's why some of them can be so picky they might even be harder to sign with than some publishers. This means you will get rejected. Even if you're thinking that's impossible right now. Do not take it as a sign that your work is terrible. (Though if you suspect that it is, maybe get a critique partner, sign up for Critique Circle, or something like it.) An agent's rejection of your idea or manuscript is simply an admission that that agent doesn't personally believe they can sell it.

If you send out a clump of queries, expect a couple immediate rejections. Positive responses usually take a little longer, but not always. The fastest positive response I ever had came 9 minutes after I'd sent the e-mail. The slowest positive response I've had was just under 2 months. (They both became full manuscript requests, but I did not ultimately sign with either agent.)

If you get a ton of rejections and never even one partial request, it might actually be your fault. They all remind you that "publishing is a subjective business," but go back to the drawing board if you have more rejections than you have fingers to count them. You might have a terrible project (or one that totally wouldn't sell right now), but you also might just be not presenting it in language that helps the agent see its potential. Submit it to Query Shark.

If the agent you queried requested sample material sent along with the query, be ready to wait a little longer. However, since most just want a query letter or a query + a few pages, what you're most likely to get next is a partial manuscript request--usually 3 chapters or 40 to 50 pages. The agent will read your partial and decide whether they want to see the whole thing. If an agent requests material, reply to the mail and/or include the original correspondence so no one is confused as to what project this is or about whether it is requested material.

If an agent does request your full manuscript, make sure you know their policies on simultaneous submissions. Most agents don't mind if you're querying many agents at once, but once they're considering the full manuscript, many want it exclusively. If that is stipulated on their website or in any communication with you, you should respect it, but even though it's polite to have your full book out to only one person at a time, it's not a rule.

Once it's full manuscript time, you're just hoping the agent will love it and offer representation. They'll usually do this by asking to phone you, so make sure your contact info is available. More often, of course, they will reject the manuscript, but usually don't do so at this stage without offering some feedback. Less often, they may be interested enough in your book to recommend a revision, stating that if you revise and resubmit they will consider you again. This is up to you, because not every agent has the same vision for your book that you do. (One request of this nature that I received off a full manuscript involved an agent responding to my fairy tale retelling by asking me to tell a different part of the fairy tale. I declined, but sometimes agents will give ideas along these lines that writers can take and run with.)

And DON'T:

There are a lot of "don'ts" above, but here are some more. Don't put copyright notifications on your work. Copyright law assures that once you've put something in a fixed form, you own the copyright, even if it isn't registered. Notifying the agent that your story is "COPYRIGHT!!!" suggests you think they might steal it. They're not interested in doing that.

Don't send an agent a manuscript you've published on the Internet, self-published, or vanity published without saying so and without making sure to the best of your ability that they would represent such a thing. First publishing rights are important and the publisher can't buy those if your book has seen print already.

Don't talk back to agents if they reject you. You may figure you might as well mouth off if they're not going to work with you, but a) you may want to query them again someday with another project; b) the publishing world can be a bit small, and you never know who might find out about your behavior; and c) it's not nice, so don't be a jerk!

Don't query to ask if you can query.

Don't query agents who say they aren't taking new clients (if it's not through personal invitation).

Don't send a manuscript attached if you haven't been told attachments are okay.

Don't send a manuscript of inappropriate genre to an agent who doesn't represent it, especially if you're planning to ramble for a while about why they should start representing this kind of book. Not only will you get rejected, but you shouldn't want that agent to represent your book if they don't already have the connections that would be necessary to sell it.

Don't repeatedly follow up on your query or your manuscript. Sometimes an agency will give you a time frame for how long you should wait before following up. But sometimes agencies will explicitly state that if you do not receive an answer, that means they're passing on your material.

Don't try to kiss the agent's butt. You're submitting your work to them and hoping they love it, sure. But just a cordial "I'm looking forward to hearing from you" is fine, while "I would be so, so grateful if you'd respond. I know you're really busy. Thank you so much for paying attention to little old me" is . . . totally not. It should go without saying that neither of you wants to waste the other's time. So describe why your work is right for them, but don't bang on about how great they supposedly are.

Don't include reviews. The agent doesn't care if your critique partner loved it and said X, because the agent knows that your crit partner is biased and that the publishing industry is, well, biased in a different way. The agent also doesn't care if you got five stars on Amazon when you self-pubbed it.

For that matter, don't praise yourself. And don't make promises. If you tell the agent how your book is totally going to outsell Harry Potter, they will probably want you to go away really quickly.

Don't make excuses for why your query sucks. You won't be excused. You may feel like you're not very good at writing queries--and you may be right--but don't tell the agent that your book is just so jam-packed with detail and complex themes that you can't possibly be expected to summarize it. Do it. You're expected to do it. Don't think that whining about how hard it is will garner sympathy.

And for the love of cheese, don't call your book a "fictional novel." It is a novel. Or it is fiction. But "fictional novel" is redundant and they will all laugh at you.

This is mostly just stuff I've learned or common sense, but there are tons of agents who blog and write articles with advice (or sometimes you can even learn from mocking).

Good luck to you. Ask me if you have a question about querying in general or my experience specifically. I'm an author who has spent some time searching for representation and succeeded, not an agent or publishing-industry professional, so please keep that in mind if you want to ask.